The antireflection film is generally disposed on the outermost surface of a display having a reflectance reduced by using an optical interference principle in an image display device such as cathode ray tube display device (CRT), plasma display panel (PDP) and liquid crystal display device (LCD), so as to prevent reflection of external light which causes reduction in the contrast or reflection of an image.
In recent years, the display of an image display device is required to have higher precision, higher luminance and higher color reproducibility and to cope with this, the antireflection film is also demanded to have more improved antireflection performance.
However, in an antireflection film having only a hard coat layer and a low refractive index layer on a transparent support, the low refractive index layer must be designed to have sufficiently low refractive index so as to reduce the reflectance. For example, in the case of an antireflection film having a triacetyl cellulose support and using a dipentaerythritol hexaacrylate UV curable film as the hard coat layer, the refractive index must be 1.40 or less for attaining an average reflectance of 1.6% or less in the range from 450 to 650 nm.
The material having a refractive index of 1.40 or less includes, as an inorganic material, fluorine-containing compounds such as magnesium fluoride and calcium fluoride, and as an organic material, fluorine-containing compounds having a large fluorine content. These fluorine-containing compounds lack, however, in the cohesion and therefore, deficient in the scratch resistance as a film disposed on the outermost surface of the display. In order to have sufficiently high scratch resistance, a compound having a refractive index of 1.43 or more is necessary.
JP-A-7-287102 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) describes a technique of increasing the refractive index of the hard coat layer and thereby reducing the reflectance. However, due to large difference in the refractive index between this high refractive index hard coat layer and the support, color irregularity is generated on the film and the dependency of the reflectance on the wavelength greatly fluctuates.
JP-A-7-333404 describes an antiglare antireflection film excellent in the gas barrier property, glare-proofing property and antireflection property, where, however, a silicon oxide film by CVD method is indispensable and therefore, the productivity is inferior to the wet coating method of forming a film by coating a coating solution.
JP-B-6-98703 (the term “JP-B” as used herein means an “examined Japanese patent publication”) and JP-A-63-21601 discloses a technique of coating a composition comprising a hydrolysis partial condensate of an alkoxysilane compound on the surface of a plastic substrate and thereby reducing the reflected light. According to this technique described in those patent publications, an inorganic film is obtained by a sol-gel process using a wet coating method. Since the film is an inorganic film, a very high film strength is expected, however, this inorganic film generally exhibits poor adhesive property to many substrates and is disadvantageously liable to cause peeling failure. Furthermore, heating for a long time is indispensable for the curing and therefore, the productivity is low.